A variety of ligand-receptor assays have been developed to detect the presence of a preselected analyte in body fluid. Typically, these assays involve antibody-antigen interactions, synthetic conjugates comprising radioactively, enzymatically, spectroscopically, or visually observable tags, and specially designed reactor chambers. In most assays, there is a receptor (e.g., an antibody) that is specific for the preselected analyte (e.g., an antigen), and a means for detecting the presence and/or amount of a resulting receptor-analyte (e.g., antibody-antigen) complex. Most current assays are designed to make a quantitative determination, but in many circumstances all that is required is a qualitative result, i.e., a positive or negative signal. Examples of such qualitative assays include, for example, pregnancy tests, ovulation tests as well as a variety of other types of urine analysis. In these tests, visually observable signals such as the presence of agglutination of a color change are preferred.
The assays optimally are performed using single-step devices wherein the only step the user need perform prior to observation of the result is application of the sample to be assayed onto the device. Single-step devices, therefore, obviate the necessity of performing, subsequent to the application of the sample, a series of manipulations which may be time consuming and/or may introduce errors in the end result. Accordingly, several single-step devices, for example those described in International Application Nos. WO 88/08534, published Nov. 3, 1988, have been developed and are commercially available.
The single-step device described in International Application Published No. WO 88/08534 comprises a hollow casing containing a porous assay material communicating with the exterior of the casing via a fluid sample receiving member. During operation, the user applies the fluid test sample onto the fluid sample receiving member protruding out of the casing. Thereafter, the fluid sample while traversing the carrier material enters the casing and moves to a capture region disposed upon the carrier material. The capture region comprises a means for binding a preselected analyte. When the fluid sample reaches the capture region, assuming that the fluid sample contains the analyte, the analyte binds to the capture region. The bound analyte subsequently can be visualized within the capture region.
It has been found, however, that invalid test results may arise from the use of single-step devices, particularly devices wherein the fluid sample is applied directly from a fluid stream through a urine inlet port defined by the casing onto assay material enclosed therein.
An improved single-step test device for detecting the presence of a preselected analyte in an urine stream is described in the above-cited U.S. Pat. Nos. 6,046,057 and 6,277,650. The device includes a hollow rectangular outer casing and an assay material disposed within co-joined upper and lower sections of the casing. The outer casing includes a urine inlet port; a viewing window in the upper section; at least the upper section consisting of transparent material; and may also include at least one drainage vent spaced about the urine inlet port. The assay material is a sorptive material including: a urine sample application region adjacent to, and in fluid communication with the urine inlet port; a capture region adjacent to the viewing window; and a fluid flow path for transporting a liquid sample between the urine sample application region and the analyte capture region. The flow of urine in the fluid path is observable through the transparent upper section for confirming a test is operative. The drainage vent is located to permit excess urine entering the casing from the urine stream to exit the casing thereby to minimize hydraulic pressure induced flooding of the assay material disposed within the casing and to reduce the frequency of false test results. In this improved device, a colloidal gold label antibody reagent is deposited on a release region of assay material. When, in this example, urine is applied to the sample absorbent material 8, the urine moves by capillary action or sorbent movement downstream toward window. When the urine contacts the reagent, it reconstitutes the reagent material, causing the reagent to move with the urine front along the flow path. When the reconstituted marker reagent passes through the window region 11, capture means are included in the capture region 85 to cause a single colored line to appear indicative of no pregnancy, or a double line to appear indicative of pregnancy. Although this device represented a very positive improvement over the prior single-step test devices, a user must interpret the lines that appear in the associated window to determine whether or not the test result is indicative of pregnancy. The present inventors recognized that if the requirement for a user to have to interpret between single colored lines and double lines can be eliminated, whereby a simple display of the word Yes+ for pregnancy, or No− for non-pregnancy, could be provided in a further improved such device, mistakes in interpretation by a user can be substantially eliminated. Note that as previously indicated above, the aforesaid two patents, and the present invention, are all commonly owned.